GRN and Atrophy: Clinically, heterozygous non-sense mutations of GRN that result in a loss of 50% of PGRN mRNA, cause FTD-GRN, a form of frontotemporal dementia that results from a progressive cortical atrophy and is, at present, almost always lethal (Baker et al., 2006; Cruts et al., 2006).